Why do you have to vent a dryer and not an oven?

An oven ought to be vented. The purpose of the range hood is to pull out the water that bakes out of the food every bit as much as to pull out grease, smoke and strong odors. Both the oven and the dryer dump moisture into the air. If that moisture is not vented out of the house it will condense on cold walls and Windows. Moisture grows mold and causes other problems. Of the two appliances, the dryer dumps many more times the volume of water vapor into the air. If both appliances are fueled by natural gas, burning the gas will also produce water vapor. Again, the oven does not use nearly a fraction of the gas that the dryer uses so the vapor can be dumped into the house without too much problem. Many houses during the winter are drier than most deserts because the moisture content of cold outside air is very low. When that air is heated, its moisture content remains the same but its relative humidity drops. If your Windows sweat, that is a good sign that excessive moisture is in your house and you need to be venting your appliances or running the exhaust fan during hot showers.